1. Field of the Invention
The present invention is directed to a monitoring circuit for an RF surgical apparatus, and in particular, to a monitoring circuit for an RF surgical apparatus having an RF power stage and a control circuit for driving the power stage.
2. Description of the Prior Art
Various types of monitoring circuits are known in the field of RF surgery, such as the "Radiotom 804" manufactured by Siemens AG. The goal of most of these monitoring circuits is to protect the patient against undesired burns when cutting and/or coagulating. Regulations in many countries, such as "Medizingeraeteferordnung" (Deutsches Bundesgesetzblatt, Volume 1985, Part I, pages 93-98, Section 3) in West Germany, require that protective measures must be undertaken in medical devices so that patients, workers or third parties are not exposed to life and health hazards given proper employment of the apparatus, commensurate with the nature of the apparatus. It is also required that surgical devices, such as RF surgery devices, be equipped with a warning means to indicate an apparatus-caused incorrect dosage. Similar requirements are found in IEC 601, Part I, Section 51.
A so-called "first malfunction" is of particular interest in an RF surgical apparatus. The term "first malfunction" means a first apparatus-caused error. Given the occurrence of a first malfunction, the set power (for example, 100 watts) which can be lower than the maximum available output power (for example, 400 watts) should not be exceeded, or should be exceeded only by a defined tolerance value (for example, 30%). For this example, the output power should not exceed 130 watts given the occurrence of such an error, for example, in the power generating means or in the control means as a consequence of the outage of a component, such as a transistor.